Integrated infrared-tracker-receiver laser-rangefinder target search and track system

ABSTRACT

For use in a fire control system, a target search and track system to which approximate azimuth and elevation information of the position of a searched target is applied, when the system is in a search mode. The information is used to cause a pointing mirror to point to the target, so that infrared energy is received therefrom, and is reflected to an infrared tracker receiver. Once infrared energy from tee target is received, the system is switched to a track mode in which the position of the pointing mirror is controlled by error signals from the receiver. The receiver includes a detector array and an oscillating, of scanning mirror which, initially, is controlled to scan the array in a wide-angle coarse track mode, in which the array is scanned over a relatively large field of view. When the target is detected near the center of the receiver field of view, the receiver is switched to a small-angle fine track mode, in which the array of detectors is scanned over a much smaller field of view, so that the receiver provides a much higher rate of pointing mirror positioning signals. The positions of the pointing mirror, about two orthogonal axes of rotation, are encoded to provide tracked target azimuth and elevation information, which is supplied to a fire control computer. A laser rangefinder is incorporated, which uses the accurately positioned pointing mirror to reflect laser light to the target and receive laser light, which is reflected by the target back to the system. The laser rangefinder provides the tracked target range information.

Sttes tent Jones et al.

[ Feb. 22, 1972 [54] INTEGRATED HNFRARED-TRACKER- PrimaryExaminer-Rodney D. Bennett, Jr. RECEIVER LASER-RANGEFINDER AssistantExaminer-N. Moskowitz TARGET SEARCH AND TRACK Attorney-James K. Haskelland Walter J. Adam SYSTEM [57] ABSTRACT [72] Inventors: Sheldon Jones,Palos Verdes Estates; For use in a fire comm] S ystem, a target searchand track g fig Briggs Los Angeles' both of system to which approximateazimuth and elevation informaal tion of the position of a searchedtarget is applied, when the 73 Assignee; Hughes Ai ft company CulverCity, system is in a search mode. The information is used to cause a mpointing mirror to point to the target, so that infrared energy isreceived therefrom, and is reflected to an infrared tracker Flledi 11969 receiver. Once infrared energy from tee target is received, the[21] AppL NOJ 849,219 system is switchedto a track mode in which theposition of the W V 7 pointing mirror lS controlled by error signalsfrom the receiver. The receiver includes a detector array and an oscil-[52] U.S. Cl. ..356/5, 250/203, 356/ 152 lating, of scanning mirrorwhich, initially, is controlled to scan [51] Int. Cl ..G01c 3/08 thearray in a wide-angle coarse track mode. in which the [58] Field ofSearch ..356/4, 5, 152; 250/199, 203 array is scanned over a relativelylarge field of view. When the target is detected near the center of thereceiver field of view, [56] References Cited the receiver is switchedto a small-angle fine track mode, in which the array of detectors isscanned over a much smaller UNIT TATE PATENT field of view, so that thereceiver provides a much higher rate 2 967 2 H1961 Blackstone et al178/6 7 of pointing mirror positioning signals. The positions of the3204l02 8/l965 pointing mirror, about two orthogonal axes of rotation,are en- 3346738 10/1967 coded to provide tracked target azimuth andelevation infor- 3480779 11/1969 mation, which is supplied to a firecontrol computer. A laser 350806l 4/1970 rangefinder is incorporated,which uses the accurately posi- 3519829 7/1970 tioned pointing mirror toreflect laser light to the target and 3464770 9 1969 receive laserlight, which is reflected by the target back to the system. The laserrangefinder provides the tracked target range information.

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8a v i i/IJ Pawn/v6 MM 7a dew/MAME; ave 2 PATENTEDFEB 22 I972 SHEET 1 OF6 INTEGRATED llNFlRARElD-TRACKER-RECEIVER LASER-RANGEFINDEIR TARGETSEARCH AND TRACK SYSTEM BACKGROUND OF THE INVENTION 1. Field of theinvention The present invention relates to a target search and tracksystem and, more particularly, to a target search and track system withinfrared tracking and laser ranging means.

2. Description of the Prior Art l-Ierebefore, in a target search and/ortrack system, such as is employed in a gun fire control system, radarsare employed to search or acquire a target. Once the target is acquiredthe radars are used to track the target. Typically, the radars trackingthe target provide target coordinates such as azimuth (AZ) and elevation(EL) and target range to a fire control 7 computer. The latter computesand provides the signal necessary to control the panting of guns as tohit the target. Two basic disadvantages characterize such a system. Thefirst disadvantage is that the precision of the tracking information,provided by such radars, is limited. Consequently, target hitprobability is low. Another disadvantage is that radars are vulnerableto electronic jamming, particularly after the target senses that isbeing tracked. Thus, a target, with sophisticated electronic jamming orcountermeasures (CM), may completely disable the fire control system.Such disadvantages can only be eliminated, or greatly minimized, byproviding a target search and track system which provides higheraccuracy of tracking information, and one which is less vulnerable toelectronic jamming, particularly after target acquisition. The lattercapability can only be provided by a target tracking system which iscovert, i.e., it does not transmit electromagnetic energy in order totrack the target, so that it does not reveal its own position.

OBJECTS AND SUMMARY OF THE INVENTION It is a primary object of thepresent invention to provide a new and improved target search and tracksystem.

Another object is to provide a new target search and track system withincreased accuracy of target tracking information.

A further object of the present invention is to provide a target searchand track system which is less vulnerable to electronic jamming thanprior art systems.

Still a further object of the invention is to provide a new targetsearch and track system in which radars may be employed for targetsearching only, with target tracking being provided by means other thanradars, which are less vulnerable to electronic jamming and whichprovide high accuracy tracking information.

Theses and other objects of the invention are achieved by providing asystem which includes an infrared tracker receiver and a laserrangefinder. The general direction of the target may be acquired eitherautomatically, such as by means of a search and track radar, ormanually, by optical sighting. A system backup mode of operation is alsoincorporated, enabling target acquisition to be accomplished by means ofa search radar only and the infrared tracker receiver, which isinitially operated in a search mode.

Once target acquisition is achieved, the target is angle tracked by theinfrared tracker receiver which controls the positioning of an opticalsystem so that the infrared energy or IR from the target is detected inthe center of the IR receivers field of view. The angular position ofthe optical system is encoded and resolved to provide target azimuth andelevation signals. A laser rangefinder, which is boresighted to the IRtracker receiver, provides target range information. The optical system,the position of which is controlled by the IR tracker receiver, is alsoused to point the laser to the target, thereby providing the highpointing accuracy which is required for the laser rangefinder.

The target azimuth, elevation and range information may be supplied to afire control computer for gun or missile control.

The azimuth and elevation information, obtained with the IR trackerreceiver is much more accurate and less noisy than the same informationderived from a radar tracker. Also. the IR tracker receiver, since itdoes not transmit electromagnetic energy to achieve target tracking, isless vulnerable to elec tronic jamming or other CM techniques. The laserrangefinder does transmit electromagnetic energy but it need not be usedin a continuous fashion until just before gun firing. Also. it does notbroadcast except over a very small angle, less than 1 milliradian,thereby making its detection for jamming purposes most difficult.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simple block diagramof aconventional, prior art fire control system;

FIG. 2 is a general block diagram of the novel system of the presentinvention;

FIGS. 3-10 are diagrams useful in explaining the operation of aninfrared tracker receiver, shown in FIG. 2;

FIGS. 11 and 12 are diagrams of circuitry used for target searching bymeans of the infrared tracker receiver; and

FIG. 13 is an optical schematic diagram of a telescope. shown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is now made to FIG. 1which represents a prior art fire control system. Typically. in such asystem a fan beam search radar, designated by block 11 and a pencilbeam-track radar, designated by block 12. are employed to search oracquire the target, as well as track it. The fan beam radar providestarget azimuth (AZ) and range (R) information to the pencil beam trackradar, which in turn provides. target azimuth, target elevation (EL) andtarget range information to a fire control computer 15. The computer 15uses this information in its computations and provides pointing commandsignals to guns which fire at the tracked target. These signals may beused to direct a missile to the tracked target.

As previously pointed out, such a system suffers from at least two basicdisadvantages. These include limited target tracking accuracy by theradars and their vulnerability to countermeasures, such as electronicjamming. These disadvantages are eliminated or at least greatlyminimized by the novel system of the present invention. In accordancewith the teachings of this invention, in some modes of the systemsoperation it is assumed that a target is searched by some external meansuntil its approximate position is acquired. Position information of theacquired target, generally in the form of target azimuth (AZ) and targetelevation (EL) are then supplied to the novel system to cause a pointingmirror to point to the general direction ofthe target, and receiveenergy which is either radiated by the target or reflected therefrom.The system is assumed to be operating in a search mode when the positionof its pointing mirror is controlled by the externally supplied targetposition information.

Once sufficient energy is received by the system to indicate thedetection of an actual target, the system is switched to a track mode inwhich the position of the pointing mirror is controlled by errorsignals, generated by an infrared (IR) tracker receiver. This receiveris operable in a coarse track mode as long as the error signals whichare generated by it are above selected threshold levels. However, oncethe error signals fall below these threshold levels, the IR receiver isswitched to a fine track mode to accurately track the target.

The position of the pointing mirror is measured to provide accuratetarget azimuth and elevation information. The system also incorporates alaser rangefinder which uses the accurately positioned pointing mirrorto direct light to the target and receive reflected light therefrom. Thelaser rangefmder provides target range information, The target azimuthand elevation information, as a function of the pointing mirror positionand the target range information from the laser rangefinder may besupplied to a fire control computer which computes and provides gunpointing commands.

The novel system of the present invention may be operated in any one ofseveral different modes in order to obtain the approximate or generalazimuth and elevation information of a searched target, which onceacquired is tracked by the system as will be explained hereafter indetail.

The novel system may be operated in a normal target acquisition mode inwhich the general azimuth and elevation information of a target isacquired by radars, such as the fan and pencil beams radars. The systemmay also be operated in a manual target acquisition mode, in which thetarget is acquired by manual optical sighting. The coordinates of thegimbal of the optical device, such as a telescope, used for sighting,may be utilized to provide the initial azimuth and elevationinformation, necessary for target acquisition. The system may further beoperated in a backup target acquisition mode of operation in which theIR receiver is used for target acquisition, as well as thereafter fortarget tracking. In any one of these modes the approximate or generalazimuth and elevation of an acquired target are obtained. The termsapproximate or general as used herein in connection with the targetazimuth and elevation intend to indicate that the azimuth and elevationare sufficient to define the general position ofa tar get so that amirror or other optical means may be made to point to it, but are notsufficient to accurately define the target position for gun controlpurposes.

Reference is not made to FIG. 2 which is a simple block diagram of thepresent invention. Therein, numerals 21 and 22 designate two inputterminals, at which the approximate azimuth and elevation angles of anacquired target are assumed to be supplied from target acquiring means.As pointed out in the normal target acquisition mode these meanscomprise conventional radars, such as the fan and pencil beam radars l1and 12, shown in FIG. 1. The terminals 21 and 22 are connected to servounits 23 ofa rotatable pointing mirror 25, through a Search/Track mode(STM) controller 26. Initially, the system is in the search mode so thatthe azimuth and elevation information of the acquired target, present atterminals 21 and 22, are supplied to servo units 23. These units adjustthe position of mirror 25 about two orthogonal axes of rotation usingthe measured gimbal positions provided by AZ and EL resolvers 45 and 46so that the mirror is in position to receive energy from the acquiredtarget.

Infrared energy or IR received from a target is directed by the mirror25 to an IR tracker receiver 30 through a telescope 35. The sametelescope and mirror 25 are used to direct light from the lasertransmitter 337 to the target, and to receive light, which is reflectedby the target back to the system and direct it to a laser receiver 38.The laser transmitter-receiver combination serve as a laser rangefinder,providing target range, R, which in a fire control system is supplied tothe fire control computer 15.

As will be described hereafter in detail, the IR tracker receiver 30upon receiving sufficient IR energy from a target to indicate thedetection of an actual target, produces an IR ON Target (IROT) signalwhich is supplied to the STM controller 26, causing the latter to switchto a track position or mode, in which two output lines 41 and 42 ofreceiver 30 are connected to servo units 23. These lines are used tosupply the servo units 23 with azimuth and elevation error signalsdesignated E and E which are produced by receiver IR, as a function ofthe detection of the target by detectors in the receiver, at other thanthe center ofits field of view. The servo units 23 use these mirrorsignals to adjust the position of mirror 25, such as by rotating itabout two axes of rotation, so that the IR energy is directed to thecenter of the receiver field of view.

As previously stated, the IR receiver is initially operated in a coarsetrack mode in which the receiver field of view is relatively large. Oncethe error signals E and E fall below selected threshold levels thereceiver is switched to a fine track mode in which a much higher rate oftracking information is produced, thereby enhancing the systems targettracking capability.

The position of the tracked target is determined in azimuth andelevation by measuring the position of the pointing mirror 25 about itstwo axes of rotation, by means of the digital encoders 47 and 48, whichare designated as the AZ encoder and the EL encoder, respectively. Theoutputs of the encoders 47 and 48 are used to determine the azimuth andelevation of the tracked target, which in FIG. 2 are shown supplied tothe fire control computer 15.

Form the forgoing it should be appreciated that in the system of thepresent invention irrespective of the manner in which a target issearched and acquired once it is acquired, and its azimuth and elevationinformation is provided to the system, the actual tracking of the targetis accomplished by the IR receiver to provide accurate target azimuthand elevation information. Range information of the tracked target isprovided by the laser rangefinder. Since the need for radars for targettracking is completely eliminated, the system of the present inventionis much less vulnerable to electronic jamming. Also, in terms oftracking, the azimuth and elevation information which is obtained withthe IR tracker receiver is more accurate and less noisy than the sameinformation derived with a conventional radar tracker.

The manner in which the IR receiver operates in its coarse and finetrack modes may best be explained in conjunction with FIGS. 3-10. Thesefigures are used to diagram circuits, necessary for the receiversoperation. The circuits are presented as examples of the type ofcircuitry necessary for the receivers operation rather than to limit tothe specific examples. In FIG. 3, T represents an acquired target fromwhich IR energy 51 is received by the pointing mirror 25. As previouslystated, the target's initial position information provided to the systemis used to position mirror 25 so that the IR energy is directed by themirror through telescope 35 to the IR receiver 30.

The receiver includes an oscillating or scanning mirror to which the IRenergy from the telescope is directed. The scanning mirror oscillates orrotates about an axis 61. If desired, the mirror 60 may be though to bepart of the telescope. The receiver includes a detector array 62 whichis located at the telescope focal plane, so that the IR energy isfocused onto a spot on or near the detectors, forming the array.

The array includes a linear array portion of an odd number of detectors,such as 9, designated D1 through D9, the center detector being D5. Thenumber of detectors in the linear array is typically odd and not lessthan three. In addition to the nine detectors in the linear array, apair of chevron detectors, designated D10 and D11, are positioned onopposite sides of the center detector, D5.

In FIG. 3, dashed line 64 designated a coarse track field through whichthe array of detectors is scanned back and forth when the mirror 60 isscanned over a wide angle, which is the case when the receiver isoperated in a coarse track mode. Dashed line 65 represents a fine trackfield through which the array is scanned back and forth when thereceiver is operated in the fine track mode. The detector array 62 isplaced in the receiver 30 so that the detectors Dl-D9 lie in the focalplane of the telescope and in a direction parallel to the axis ofrotation 61. However, for explanatory purposes only in FIG. 3 theyappear to lie in a plane perpendicular to axis 61.

Basically, it is assumed that when the system is first turned on thereceiver operates in the coarse track mode. After the mirror 25 isinitially positioned to reflect IR from the target T to the scanningmirror 60, the array is scanned through the coarse track or wide-anglefield 64 and IR from the target is sensed by one of the detectors in thearray. The scanning mirror 60 may be thought of as going through a nullor zero position during each scanning cycle. For the particulararrangement, shown in FIG. 35, it should be appreciated by thosefamiliar with the art that only when the mirror is perfectly positionedabout an axis, perpendicular to the plane of the figure, will IR from atarget be detected by one of the detectors when the scanning mirror 60is at its null or zero position. In such a case the target is detectedat or near the center of the field.

If however, the mirror 25 is at other than such a position, the IR fromthe target will be sensed by one of the detectors in the linear arraywhen the position of the mirror 60 is other than its null position.Thus, the position of the scanning mirror, when the target is detectedby one of the detectors in the linear array, is an indication of theerror in the position of the reflecting mirror 25 with respect to itsnormal zero azimuth position, which is at 90 to the telescope axis. Thisangle of the scanning mirror which is represented by X may be thought ofV as an error in azimuth (AZ) or simply as azimuth error E It should befurther appreciated, that the particular detector in the linear arraywhich senses the target is an indication of an error in the position ofmirror 25 about its vertical (in the plane of paper) axis of rotation,which is designated in FIG. 3 by array Y. This error may be thought ofas error in elevation (EL), or simply an elevation error, E

As will be described hereafter in detail, the IR receiver includescircuitry to generate voltages which are indicative of the scanningmirror positions. These voltages are then util ized to derive the errorsin both azimuth and elevation which are supplied to the servo units 23to adjust the position of the mirror 25 with respect to its two axes ofrotation, and cause the target energy to be detected near the center ofthe field of View.

The receiver 30 is assumed to include a wide-angle scan generator (seeFIG. 4) and a small-angle scan generator '78 which produce sawtoothsignals, designated 75s and 763, respectively. The two signals are ofequal slopes or rat is except that they differ in amplitude and,consequently, in frequency. It is the output of either one of thesegenerators which is supplied to an amplifier through an adder 82, Theoutput of the amplifier is used to control the rotation of the mirror 60to cause it to scan the detector array. When the output of generator 75is supplied, the scanning mirror 60 scans the array back and forththrough the wide field 64 (see FIG. 3), while scanning the same arrayback and forth through the smaller field 65, when the output ofgenerator 76 is supplied to the amplifier.

Since the position of the scanning mirror 60 is measured by an ACtransducer, a phase sensitive demodulator is incorporated to provide anDC output, designated E which is supplied to the adder 82. The magnitudeof E indicates the rela tive position of the scanning mirror 60 withrespect to its null position, while the polarity of E indicates thedirection with respect to the null position.

The relative magnitude and polarity of E as a function of mirror ddposition are diagrammed in FIG. 5 and are represented by the straightline 90. From FIG. 5 it should thus be appreciated that E increases inamplitude as the position of scanning mirror 60 increases from its nullposition. The signal 5,, is of a first polarity. such as positive whenthe scanning mirror is to the right of its null position while having anegative polarity when the mirror is to the left of its null position.The null position is represented in FIG. 5 by numeral 92.

Reference is now made to FIG. 6 which is a simplified block diagram ofcircuitry capable of producing the azimuth, E in the IR receiverincorporated in the present invention. As shown, each of the ninedetectors D1-D9 in the linear array has associated therewith anamplifier and a threshold circuit. The outputs of the threshold circuitsare connected to an OR- gate 95. For simplicity, only amplifiers 101,and 109 and threshold circuits 111i, 115 and 119, associated withdetectors D1. D5 and D9 respectively, are shown. In the coarse track orwide-angle mode, the output of the OR-gate 95 is supplied to holdcircuit to which the voltage E is supplied.

The output of OR-gate 95 is also supplied to a counter 121v This counteris incremented by one each time gate 95 IS enabled. When severalsuccessive energy detections are sensed by the detectors, therebyindicating that a real target pro\ ides the IR energy. the count in thecounter reaches a selected value and it provides an IR ON Target (IROT)pulse which is supplied to the STM controller 26, switching the latterto the track mode. In this mode it is the error signals from the IRreceiver 3! which are used to control the position of mirror 25. Thus.the function of the counter 121 is to insure that switching from thesystem search mode to the track mode occurs when sufficient IR energy isreceived by the receiver's detectors from a real target. To insure thatspurious noise does not contribute to the production of the IROT signal,the counter 121 may preferably include a circuit which resets thecounter if greater than a selected interval elapses between outputs ofOR-gate 95. 7' '7 Whenever a target is sensed by any of the ninedetectors and its output exceeds the threshold ofits associatedthreshold cir cuit, the ORgate 95 is enabled, triggering the holdcircuit 120 to hold or store the E voltage. Thus, the voltage in thehold circuit indicates the scanning mirror position at the timeofdetection. This voltage, after filtering by a filter 122, representsthe position error in the track mode this error signal is supplied tothe servo units 23 via line 41 to adjust the position of mirror 25 aboutits perpendicular axis of rotation, to bring the target to the center ofthe field in the X-axis. It should be clear that, since in the finetrack or small-angle mode the field in cludes only detectors D5, D10 andD11, in this mode, the azimuth error is produced by the output of D5.Thus, in this mode it is the output ofcircuit 115 which is supplied totrigger the hold circuit 120,

From the foregoing it should be appreciated that for the determinationof E at least in coarse track mode, it is not significant which of thedetectors in the linear array senses the target, since the ninedetectors are in a line perpendicular to the scanning axis (X) alongwhich the error is detected. This however, is not the case when theerror in the Y-axis or in elevation, E is to be determined. Such erroris directly related to the detector which senses the target and theposition of the detector in the linear array. It is apparent from FIG. 3that if the target T is detected by D1 it indicates a maximum E in afirst direction from the center, while a maximum E in the oppositedirection is indicated when D9 detects the target.

The elevation error. E may be produced by a circuit, as shown in FIG. 7.Basically, in the elevation-error-producing circuit, the output of eachof detectors Dl-D4 and D6-D9 is connected through a one shot to acorresponding resistor in a weighted resistor matrix 125, which isconnected to the input of an amplifier 126. The output of the amplifier126 represents E in the coarse track mode. The eight one shots aredesignated 131-134 and 136l39, while the resistors are designated bynumerals 141-144 and 146-149.

Also forming a part of the matrix is a resistor 150, which is connectedto a fine elevation error-producing circuit 155. which is diagrammed indetail in FIG. 8. Ignoring for a moment circuit 155, the resistor matrixis weighted so that the amplitude and polarity of the voltage toamplifier 126 indicate which of the eight detectors D1D4 and D6-D9senses the target, thereby indicating the E magnitude and polarity orsense with respect to the field center. For example, the matrix may beweighted so that when D1 senses the target, +4 volts are supplied to theamplifier, while 4 volts are supplied when the target is sensed by D9.Also, +3 volts and -3 volts are produced when the target is detected byD2 and D8, respectively, +2 volts and 2 volts when D3 and D7.respectively sense the target, while +l volt and l 1 volt are producedwhen the target is sensed by D5 and D6. respectively.

The output, E of this circuit is assumed to be supplied to servo units23 (FIG. 2) to rotate the mirror 25 about its vertical axis of rotationto reduce the elevation error until the target is detected by the centerdetector D5. It is circuit 155 which generates E when the target isdetected by D5. Its (circuit 155) output is supplied and combined in theresistor matrix 125 to insure that in the coarse track mode, theelevation error E is continuously reduced until the target is detectedby D5. In the fine track or small-angle mode it is the output of circuit155, after amplification by amplifier 157, which represents E Amplifier157 is connected to circuit 155 through a resistor 158.

Reference is now made to FIG. 8 which is a simple diagram of circuit155. The circuit is shown to include three hold circuits 161, 162 and163 which are independently triggered by the outputs of D5, D11 and Dwhen the latter sense a target, to store or hold E supplied thereto. Thevoltage held in 161 is subtracted from the voltage held in 162, by asubtractor 164. The subtractor output is supplied to a second subtractor165. In 165, a fixed bias voltage is subtracted from the output ofsubtractor 124 and the resultant is the fine E when the scanning mirror60 scans the field to the right.

In an analogous arrangement the voltage in 161 is subtracted in asubtractor 168 from that in hold circuit 163. A negative bias voltage issupplied to a subtractor 128 is subtracted from the negative biasvoltage. It is the output voltage of subtractor 169 which represents thefine E when the scanning mirror 60 scans the field to the left.

The operation of the circuit 155 may best be explained in conjunctionwith FIG. 9 which is an expanded view of detectors D5, D10 and D11, andin conjunction with FIG. 5 which, is the E vs MIRROR POSITION graph. InFIG. 8, dashed line 170 represents zero elevation error, line 171represents a positive E in which the target is detected above the fieldcenter, and line 172 represents a negative E in which the target isdetected below the field center,

Let it be assumed for a moment that the azimuth error, E is zero, that Eis zero and that the mirror 60 scans to the right. In such a case whenthe target is detected by D5, at point 173, E is zero, since zeroazimuth error is assumed. However, when the target is detected by D11 atpoint 174, E is not zero. Rather, it equals a voltage depending on thefixed distance between points 173 and 174 and, therefore, the voltage isa function of the degree of angular rotation of the scanning mirror 60which is required from its null position to direct the target to D11.Let it be assumed that this mirror position is as indicated by point 175in FIG. 5. Consequently, when D11 detects the target at point 134 when Eis zero, E is positive and is equal to E For explanatory purposes let E=+4 volts. In such a case the fixed bias voltage which is applied tosubtractor 165 (FIG. 8) is +4 volts.

With the foregoing assumptions it should be seen that when the target isdetected by D5 at point 173 E ,,=O. Thus, 0 volts are held in circuit161. Then when the target is detected by detector D11 at 174, E =+4volts. Consequently, +4 volts are held in circuit 162. Therefore, theoutput of subtractor 164 is +4(+O)=+4 volts. However, due to the +4volts bias voltage which is applied to subtractor 165, the output of thelatter is +4(+4)=O volts, thereby indicating zero elevation error.

If, however, a positive elevation error is present (see line 171 in FIG.9), when the target is detected by D11 at point 177, E is greater than+4 volts. Consequently, the output of subtractor 164 is greater than the+4 volts bias, applied to 165. As a result, a net positive voltage isproduced. The magnitude and polarity of this voltage indicate themagnitude and sense or direction of elevation error E Likewise, if anegative elevation error is present (see line 172 in FIG. 9), when thetarget is detected by D11 at point 178, E is less than +4 volts.Consequently, the output of subtractor 164 is less than +4 volts, sothat when the +4 volts bias is subtracted therefrom in 165, a negativevoltage is produced, indicating a negative elevation error.

The performance of the hold circuits 161 and 163 and subtractors 168 and169 is fully analogous, for providing the fine E when scanning is to theleft. Basically, the negative bias voltage which is applied tosubtractor 169 is chosen to equal E when the target is detected by D10at point 181, in the absence of an elevation error, so that the netoutput of subtractor 169 is zero. In the particular example, thisnegative bias voltage is 4 volts.

Herebefore, it has been assumed that the azimuth error, E is zero. Itshould be pointed out that any azimuth error which may be present doesnot affect the production of the fine elevation error. An azimuth errorcauses hold circuit 161 to store an E equal to other than zero, when thetarget is detected by detector D5. However, the value of the E stored ineither circuit 162 or 163, depending on the scan direction, is shiftedby an equal magnitude, which after subtraction by subtractor 164 or 168cancels out. Thus, any azimuth error has no effect on the fine E whichcircuit 155 is capable of providmg.

In operation, when the system is firstturned on it is in the Search modeso that the azimuth and elevation information of the acquired target aresupplied to the servo units 23. At the same time the receiver 30 is inthe coarse track mode. When sufficient IR energy is detected within aselected interval, thereby indicating that the energy is from a realtarget, the counter 121 provides the IROT signal. As a result,controller 26 (FIG. 2) switches the system to the track mode. Duringthis period the receiver operates in the coarse track or wide-anglemode, as represented by the positions of switches 182, 183 and 184,shown in FIGS. 4, 6 and 7, respectively. The mechanical switches arepresented as a simple example of devices for switching the receiver fromthe coarse track mode to the fine track mode. It is clear, however, thatin practice, such mechanical switches may be too slow and thatelectronic switching would be employed. In these switches, when theswitch arms are in contact with the C terminals, the coarse track modeis performed, while in the fine track or small-angle mode the arms arein contact with the F terminals.

When the receiver is in the coarse track mode, the output of generator75 (FIG, 4) is used to rotate the mirror 60 to scan the detector arrayback and forth over the wide or coarse track field 64 (FIG,. 3). Azimutherror, E is produced by the circuit, shown in FIG. 6, while elevationerror, E is produced by the circuit shown in FIG. 7. These errors aresupplied to the servo units 23, via lines 41 and 42 respectively (FIG.2), to adjust the position of mirror 25 to direct the target to thefield center. Only when both errors fall below selected thresholdlevels, is the receiver 30 switched to the fine track or smallanglemode. The positions of mirror 25 about its axes of rotation are encodedby encoders 47 and 48 which provide highly accurate coordinateinformation of the tracked target.

The signal which is necessary to switch the receiver 30 from the coarsetrack mode to the fine track mode may be provided by the output of acircuit, shown in FIG. 10, to which reference is now made. Basically,the circuit may include two comparators 191 and 192 to which theabsolute values of E and E are respectively supplied. In each, the erroris compared with a fixed threshold level. The outputs of the twocomparators are connected to an AND-gate 193. Only when both errors fallbelow the threshold levels with which they are compared is gate 193enabled, to provide a coarse track to fine track switching controlsignal, to the various switches.

Once the receiver is switched to the fine track or smallangle mode, thefield is limited to that shown in FIG. 3 by line 65. In this fine trackmode the azimuth error is provided by the output of hold circuit (FIG.6) when the target is detected by detector D5, while the elevation erroris derived by the output of circuit (FIG. 8), as a function of themirror positions, represented by E at the times of target detection bydetectors D5, D10 and D11.

In the foregoing, only the circuitry in the receiver 30, which is usedin its coarse and fine tracking modes has been described. This circuitryis sufficient when target acquisition is accomplished by eitherconventional radars which is regarded as the system normal targetacquisition mode, or by manual optical sighting, which is regarded asthe system manual target acquisition mode. In either of these two modes,signals, representing the azimuth and elevation of the acquired target,are applied to terminals 21 and 22 (FIG. 2) to position the mirror 25,so that energy from the target is directed to the receiver 30, to enableit to first track the target in the coarse track mode and, thereafter,in the fine track mode.

As previously pointed out, the system of the present invention mayfurther be operated in a system backup target acquisition mode, in whichthe IR receiver 30 participates in target acquisition. To provide such acapability the system of the present invention includes additionalcircuitry which may best be explained in conjunction with FIGS. 11 and12. Basically, for the backup target acquisition mode of operation, thesystem includes a search signal generator (SSG) 190 (FIG. 11), an adder191 and a three position switching arrangement 192 (FIG. I2), whichreplaces the two position switching arrangement 142, shown in FIG. 4.

In the system backup mode, the switching arrangement 192 is in contactwith a terminal S (for search) rather than with either terminal C towhich the wide-angle scan generator 75 is connected, or with terminal Fto which the small-angle scan generator 76 is connected. A null positionbias source 193 is connected to terminal S, to provide a null positionbias voltage, such as volts, so that in the system backup mode, duringtarget search or acquisition, the mirror 60 is prevented fromoscillating, and is held stationary at its null position.

The Search signal generator (SSG) 190 generates two signals withdifferent waveforms. One signal, designated by numeral 195. has asawtooth waveform, while the other, designated by numeral I96, has astaircase waveform. Generators like the SSG I90 are will known in theradar art, in which they are used when bar searching techniques areemployed.

In the present system the sawtooth signal 195 is combined. in adder I91,with an azimuth signal from the conventional fan beam radar, which isassumed to acquire the target and provide an approximate target azimuthposition. The output of the adder I91 is supplied to terminal 21 (FIG.2). Thus, this output causes the pointing mirror to move back and forthin azimuth about a point generally defined by the azimuth signal fromthe fan beam radar. As the mirror 25 scans the general target positionin azimuth, the staircase signal 196 is applied, as an elevation signal,to terminal 22. This signal causes the mirror 25 to step in elevation asit scans the target position in azimuth. It should again be stressedthat during this target searching operation the scanning mirror 60 isstationary, and it is pointing mirror 25 which is rotated in azimuth andstepped in elevation until the target is acquired in its field of view,and IR energy from the target is detected by one of the detectors inreceiver 30. Such target detection is represented by an output fromOR-gate 95 (FIG. 6).

In accordance with the teachings of the invention, the first output ofthe OR-gate 95 is used to stop the target searching operation byproviding a STOP signal to the SSG 190. The output of the OR-gate 95 mayalso be used to provide the switching arrangement 192 (FIG. 12) with acontrol signal to switch from the S-terminal to the Cterminal andthereby cause the scanning mirror 60 to start scanning the detectorarray in the coarse track mode.

As previously pointed out, spurious noise may activate one of thedetectors which may result in a single output of OR-gate 95. In order toprevent such a single output from indicating an acquired target, counter121 (FIG. 6) is incorporated. When the IR receiver is used for targetsearching it may be desirable to include a simple circuit to reactivatethe the SSG 190 and switch arrangement 192 (FIG. 12) back to terminal S,if one output from gate 95 is not followed by a second output within aselected interval. Any one of conventional design techniques may beemployed in the implementation of such a circuit to provide thereactivating signal, Thus, if as a result of noise or other undesiredsource OR gate produces a single output which is not due to thedetection of IR energy from a real target, since such a single outputwill not be followed by another output, the SSG I90 will be reactivatedto continue the Search operation until a real target is detected.

From the foregoing it should be appreciated that irrespective of thesystem mode for acquiring the target, once a target is acquired,tracking is performed by the IR receiver 30. Initially, the receiveroperates in a coarse track mode. Then. when the target is tracked anddetected near the center of the array, the receiver is switched to afine track mode, in which a much smaller field of view is scanned.Consequently. a much higher rate of tracking data is produced therebyincreasing the accuracy with which the pointing mirror 25 is positioned.Thus, highly accurate position information of the track target isprovidable by the system of the present invention. The azimuth andelevation information of the track target are provided by the encoders47 and 48. When employed in fire control system, the azimuth andelevation information is supplied to the fire control computer 15, whichin turn computes and provides pointing commands for guns, aimed to hitthe tracked target.

Since the receiver 30 tracks a target by detecting IR energy receivedtherefrom, it is estimated that the IR receiver will track a hot pointin the target plume at a small distance behind the target's tailpipe.The displacement of this point from the vulnerable area of the targetmay be calculated by the fire control computer IS. The latter may besupplied with a plume bias signal to compensate for the distance betweenthe track point on the target behind its tailpipe and its vulnerablearea Attention is now directed once more to FIG. 2. There-from. and fromthe foregoing description it should be appreciated that the pointingmirror 25 and the telescope 35 are used to direct light from the lasertransmitter 37 to the target and receive light reflected therefrom anddirect it to the laser receiver 38, in addition, to their use indirecting IR energy. received from the target, to the IR receiver 30.The use of a single telescope and a single pointing mirror 25 arepreferable since they represent the minimum which is required to directIR energy from the tracked target to the receiver and laser light fromthe transmitted to the target and, therefrom. back to the receiver.Also, by utilizing the single pointing mirror 25 which is made to pointto the tracked target with a very high degree of accuracy. the highaccuracy, required for pointing the laser light for rangefindingpurposes is attained.

The use of laser transmitter-receiver combinations for laserrangefinding are well known in the art, and therefore the lasertransmitter and the receiver will not be described in any furtherdetail. However, an example of the optics of a single telescope, such astelescope 35, which is used for the direction of laser light from thetransmitter to the target. and light received therefrom to the laserreceiver, as well as directing IR energy from the pointing mirror 25 tothe receiver 30 will now be described.

Reference is now made to FIG. 13 which is an optical schematic diagramofthe telescope 35. Selected portions ofoptical elements of thetelescope have been removed in order to clearly indicate the paths ofenergy therethrough. Therein. elements. previously referred to aredesignated by like numerals. Basically, a beam of light, designated bynumeral 200. which is provided by the laser transmitter 37 is reflectedby means ofa prism 201 to a prism element 202 in the telescope 35. Thebeam is then directed through the telescope-focusing lense 204 to thepointing mirror 25, which points the laser transmitter beam 200 to thetarget T. The same pointing mir ror 25 is used to receiver both IRenergy and light from the target. The combined light and IR energy arerepresented in FIG. 13 by lines designated by numerals 210.

The combined light and IR energy are reflected by the mirror 25 to atelescope-concave reflecting member 212. The detector array 22 of thereceiver 30 is assumed to lie in the focal plane of member 212. The IRenergy and the light from a member 212 are reflected by a telescopeoptical element 214 towards a dichromatic filter element 215. Thefunction of the latter is to separate the IR energy from the laser lightby permitting the former to pass therethrough to the scanning mirror 60.In FIG. 13, the IR energy is represented by numeral 200.

While the filter 215 permits the IR energy to be directed therethroughto the scanning mirror 60 it reflects the light,

lOl024 U593 Ill which is directed thereto, through an opening in theoptical element 214, to the prism 202 for reflection to the laserreceiver 38. In FIG. 13, numerals 221 designate the light reflected byfilter 215, while the laser light beam received by the receiver 38 isdesignated by numerals 225. From FIG. 13 it should thus be apparent thatthe telescope 35 comprises a single barrel telescope which is used toreflect a laser beam, provided by the laser transmitter 37, to thetarget T, as well as to receive both reflected light therefrom and IRenergy. By the utilization of the filter 215 the two types of energy areseparated, with the IR energy being directed to the scanning mirror 60,while the laser light is reflected to the laser receiver 38.

The foregoing description may thus be summarized as comprising a novelsystem in which target tracking is accomplished by means of an IRreceiver to provide accurate tracked target position information, suchas azimuth and elevation, The system further includes a laserrangefinder, consisting of a laser transmitter and laser receiver, whichare used to provide tracked target range information. Preferably, acommon or single telescope and a single pointing mirror are used todirect the laser light from the laser transmitter to the target, as wellas to receive, both reflected laser light and IR energy, provided by thetarget. The IR receiver is operable in a coarse track mode in which afirst rate of tracking data is supplied until the target is tracked anddetected near the center of the field of view of a detector array in theIR receiver. When such detection is accomplished, the IR receiver isautomatically switched to a fine track mode of operation in which a muchhigher rate of tracked target position information is provided, togreatly increase the target tracking accuracy.

In terms oftracking, the tracked target position information which isproduced by the novel system of the present invention is significantlymore accurate and less noisy then similar information derived fromconventional radar target trackers. Also, the novel system of thepresent invention is less vulnerable to electronic jamming since it issubstantially covert, i.e., it does not transmit electromagnetic energyin tracking the target and, therefore, it does not reveal its ownposition. As previously indicated the laser rangefinder does transmitelectromagnetic energy. However, it need not be operated in continuousfashion during tracking. Rather, it may be turned on just before gunfiring. Also, the radiation of the energy is over a very small angle,generally, less than 1 milliradian. Thus, the detection and the jammingof such a laser rangefinder represents a most difficult problem.

As is appreciated from the foregoing description, for the novel systemof the present invention to operate, the general or approximate positioninformation, such as azimuth and elevation of the searched or acquiredtarget must be provided thereto. In the system normal target acquisitionmode of operation, such information is assumed to be supplied fromconventional fan and pencil beam radars. In the manual acquisition mode,such information is assumed to be supplied from gimbal angles ofamanually positionable optical sighting devicev Thus, the presentinvention may be used with radars which are employed only for searchingand acquiring a target in the systems field of view. If however, suchradar is not operable for some reason, such as for example due toelectronic jamming or other counter measures, the system may be operableby manual target acquisition.

As previously explained in conjunction with FIG. 11 and 12, the novelsystem of the present invention may be operated in a system backuptarget acquisition mode, in which the system itself is used for targetacquisition or searching, as well as for target tracking. In the backupmode, it is assumed that azimuth information of an acquired target isprovided, such as from a fan beam search radar. In this mode, the systemis operated to use this information (see FIG. 11) in searching for thetarget, by controlling the position of the pointing mirror 25, until IRenergy from the target is detected by the IR receiver from the system.Once the target is detected, the system continues to perform itstracking function as in either of the other two system modes of targetacquisition, namely, the normal target acquisition mode or the manualtarget acquisition mode.

Although particular embodiments of the invention have been described andillustrated herein, it is recognized that modifications and variationsmay readily occur to those skilled in the art and consequently it isintended that the claims be im terpreted to cover such modifications andequivalents.

What is claimed is:

1. A target search and track system comprising:

mode control means for controlling said system to operate in either asearch mode or a track mode;

optics means for controlling the direction of transmission and receptionof energy and including a positionable optical member;

position control means for controlling the position of said opticalmember; means for receiving signals indicative of the position of atarget to be tracked and for applying said signals to said positioncontrol means, when said system is in said search mode, to control theposition of said optical member;

receiving means coupled to said optics means and including an array ofinfrared energy detectors and a scanning mirror and means forcontrolling the scanning of said detectors by said scanning mirror to beover a wide field of view when the infrared energy is detected by one ofsaid detectors at a point outside a selected area from the center ofsaid field of view and for controlling the scanning of said detectors bysaid scanning mirror to be over a small field of view when the infraredenergy is de' tected at a point from the center within said selectedarea;

means for applying a switching control signal to said mode control meansfrom said receiving means to switch said system to operate in said trackmode when infrared energy from said target is detected by said receivingmeans;

means for applying positioning signals to said position control meansfrom said receiving means when said system is in said track mode tocontrol the position of said optical member so that infrared energy isdetected by said receiving means at the center ofa field of viewthereof;

means for measuring the position of said optical member;

and

laser rangefinding means for directing laser energy to said targetthrough said optics means and for receiving laser energy reflected bysaid target therethrough to provide target range information.

2. The arrangement as described in claim 1 wherein said optics meansincludes a single telescope and said optical member comprises a singleenergy reflecting mirror, said telescope including means for directinginfrared energy, which is received from said target and which isreflected to the telescope by said single mirror, to said receivingmeans, said telescope further including means for directing laser lightfrom said laser ran gefinding means to said mirror for reflection to thetarget and means for directing laser light, reflected back by the targetto the mirror to said laser rangefinding means.

3. In combination with a fire control computer of the type providingpointing commands as a function of azimuth, elevation and rangeinformation of a tracked target supplied thereto, a target search andtrack system comprising:

mode control means for controlling said system to operate in either asearch mode or a track mode;

optics means including a positionable optical member;

position control means for controlling the position of said opticalmember;

means coupled to said optics means for receiving signals indicative ofthe position of a target to be tracked and for applying said signals tosaid position control means, when said system is in said search mode, tocontrol the position of said optical member to direct infrared energy tosaid receiving means;

receiving means coupled to said optics means and including an array ofinfrared energy detectors and a scanning mir- IOI024 0594 ror and meansfor controlling the scanning of said detectors by said scanning mirrorto be over a wide field of view when the infrared energy is detected byone of said detectors at a point outside a selected area from the centerof said field of view and for controlling the scanning of said detectorsby said scanning mirror to be over a small field of view when theinfrared energy is de' tected at a point from the center within saidselected area;

means for applying a switching control signal to said mode control meansfrom said receiving means to switch said system to operate in said trackmode when infrared energy from said target is detected by said receivingmeans;

means for applying positioning signals to said position control meansfrom said receiving means when said system is in said track mode tocontrol the position of said optical member so that infrared energy isdetected by said receiving means at the center ofa field of viewthereof;

means for measuring the position of said optical member and'forproviding said fire control computer with target azimuth and elevationinformation, as a function thereof; and

laser rangefinding means for directing laser energy to said targetthrough said optics means and for receiving laser energy reflected bysaid target therethrough to provide target range information to saidcomputer.

4. The arrangement as described in claim 3 wherein said optics meansincludes a single telescope and said optical member comprises a singleenergy reflecting mirror, said telescope including means for directinginfrared energy, which is received from said target and which isreflected to the telescope by said single mirror, to said receivingmeans, said telescope further including means for directing laser lightfrom said laser rangefinding means to said mirror for reflection to thetarget and means for directing laser light, reflected back by the targetto the mirror, to said laser rangefinding means.

5. A target search and track system comprising:

mode control means for controlling said system to either operate in asearch mode or to operate in a first or a second track mode;

optical means for transmitting and receiving energy and for directingthe direction in space of which energy is transmitted or received;position control means coupled to said mode control means forcontrolling the position of said optical member;

means coupled to said optical means for receiving signals representativeof the position of a target to be tracked and for applying said signalsto said mode control means to control the position of said opticalmember;

receiving means coupled to said optical means and including an array ofinfrared energy detectors and a scanning mirror and means forcontrolling the scanning of said detectors over a wide field of view forsaid first track mode or over a small field of view for said secondtrack mode;

means responsive to infrared energy being detected by said receivingmeans for applying a switching control signal to said mode control meansfrom said receiving means to switch said system for operation in eithersaid first or said second track mode; means for applying positionsignals to said position control means from said receiving means whensaid system is in said track mode to control the position of saidoptical member so that infrared energy is detected by said recen ingmeans substantially at the center of a field of view thereof; and laserrangefinding means coupled to said optical means for directing laserenergy to said target and for receiving laser energy reflected by saidtarget therethrough to provide target range information. 6 Thecombination of claim wherein said optical means comprises a singleenergy reflecting mirror structure for receiving energy reflected fromsaid target and for directing W laser energy transmitted to said targetand for receiving laser energy reflected back from said target. V

7. system for searching in a search mode and tracking a target in afirst tracking mode or a second tracking mode com prising:

optical means including a positionable optical member for controllingthe direction of receiving infrared energy and the direction oftransmitting and receiving of laser ener mode control means coupled tosaid position control means for controlling said system to operate ineither said search mode or in one of said first and second tackingmodes;

a source of searching signals coupled to said mode control means todirect said optical member when said system is in said search mode;

receiving means coupled to said optical means and to said mode controlmeans to control the position of said optical member when said system isin said track mode. said receiving means including an array ofinfraredenergy detectors and scanning means for controlling the scanning of saiddetectors with the infrared energy received by said optical means so asto respectively provide during opera tion in said first and secondtracking modes a wide field of view or a narrow field of view of thetarget area as a function of the position that the energy is detectedrelative to the pointing direction of said optical member;

means coupled between said receiver means and said mode control meansfor applying switching control signals thereto as a function of thedetection of infrared energy so that said system operates either in saidsearch mode or in one of said first and second track modes; and

laser rangefinding means coupled to said optical means for directinglaser energy to said target through said optical means and for receivinglaser energy reflected from said target therethrough to provide targetrange information.

1. A target search and track system comprising: mode control means forcontrolling said system to operate in either a search mode or a trackmode; optics means for controlling the direction of transmission andreception of energy and including a positionable optical member;position control means for controlling the position of said opticalmember; means for receiving signals indicative of the position of atarget to be tracked and for applying said signals to said positioncontrol means, when said system is in said search mode, to control theposition of said optical member; receiving means coupled to said opticsmeans and including an array of infrared energy detectors and a scanningmirror and means for controlling the scanning of said detectors by saidscanning mirror to be over a wide field of view when the infrared energyis detected by one of said detectors at a point outside a selected areafrom the center of said field of view and for controlling the scanningof said detectors by said scanning mirror to be ovEr a small field ofview when the infrared energy is detected at a point from the centerwithin said selected area; means for applying a switching control signalto said mode control means from said receiving means to switch saidsystem to operate in said track mode when infrared energy from saidtarget is detected by said receiving means; means for applyingpositioning signals to said position control means from said receivingmeans when said system is in said track mode to control the position ofsaid optical member so that infrared energy is detected by saidreceiving means at the center of a field of view thereof; means formeasuring the position of said optical member; and laser rangefindingmeans for directing laser energy to said target through said opticsmeans and for receiving laser energy reflected by said targettherethrough to provide target range information.
 2. The arrangement asdescribed in claim 1 wherein said optics means includes a singletelescope and said optical member comprises a single energy reflectingmirror, said telescope including means for directing infrared energy,which is received from said target and which is reflected to thetelescope by said single mirror, to said receiving means, said telescopefurther including means for directing laser light from said laserrangefinding means to said mirror for reflection to the target and meansfor directing laser light, reflected back by the target to the mirror tosaid laser rangefinding means.
 3. In combination with a fire controlcomputer of the type providing pointing commands as a function ofazimuth, elevation and range information of a tracked target suppliedthereto, a target search and track system comprising: mode control meansfor controlling said system to operate in either a search mode or atrack mode; optics means including a positionable optical member;position control means for controlling the position of said opticalmember; means coupled to said optics means for receiving signalsindicative of the position of a target to be tracked and for applyingsaid signals to said position control means, when said system is in saidsearch mode, to control the position of said optical member to directinfrared energy to said receiving means; receiving means coupled to saidoptics means and including an array of infrared energy detectors and ascanning mirror and means for controlling the scanning of said detectorsby said scanning mirror to be over a wide field of view when theinfrared energy is detected by one of said detectors at a point outsidea selected area from the center of said field of view and forcontrolling the scanning of said detectors by said scanning mirror to beover a small field of view when the infrared energy is detected at apoint from the center within said selected area; means for applying aswitching control signal to said mode control means from said receivingmeans to switch said system to operate in said track mode when infraredenergy from said target is detected by said receiving means; means forapplying positioning signals to said position control means from saidreceiving means when said system is in said track mode to control theposition of said optical member so that infrared energy is detected bysaid receiving means at the center of a field of view thereof; means formeasuring the position of said optical member and for providing saidfire control computer with target azimuth and elevation information, asa function thereof; and laser rangefinding means for directing laserenergy to said target through said optics means and for receiving laserenergy reflected by said target therethrough to provide target rangeinformation to said computer.
 4. The arrangement as described in claim 3wherein said optics means includes a single telescope and said opticalmember comprises a single energy reflecting mirror, said telescopeincluding means for directing infrared energy, which is rEceived fromsaid target and which is reflected to the telescope by said singlemirror, to said receiving means, said telescope further including meansfor directing laser light from said laser rangefinding means to saidmirror for reflection to the target and means for directing laser light,reflected back by the target to the mirror, to said laser rangefindingmeans.
 5. A target search and track system comprising: mode controlmeans for controlling said system to either operate in a search mode orto operate in a first or a second track mode; optical means fortransmitting and receiving energy and for directing the direction inspace of which energy is transmitted or received; position control meanscoupled to said mode control means for controlling the position of saidoptical member; means coupled to said optical means for receivingsignals representative of the position of a target to be tracked and forapplying said signals to said mode control means to control the positionof said optical member; receiving means coupled to said optical meansand including an array of infrared energy detectors and a scanningmirror and means for controlling the scanning of said detectors over awide field of view for said first track mode or over a small field ofview for said second track mode; means responsive to infrared energybeing detected by said receiving means for applying a switching controlsignal to said mode control means from said receiving means to switchsaid system for operation in either said first or said second trackmode; means for applying position signals to said position control meansfrom said receiving means when said system is in said track mode tocontrol the position of said optical member so that infrared energy isdetected by said receiving means substantially at the center of a fieldof view thereof; and laser rangefinding means coupled to said opticalmeans for directing laser energy to said target and for receiving laserenergy reflected by said target therethrough to provide target rangeinformation.
 6. The combination of claim 5 wherein said optical meanscomprises a single energy reflecting mirror structure for receivingenergy reflected from said target and for directing laser energytransmitted to said target and for receiving laser energy reflected backfrom said target.
 7. A system for searching in a search mode andtracking a target in a first tracking mode or a second tracking modecomprising: optical means including a positionable optical member forcontrolling the direction of receiving infrared energy and the directionof transmitting and receiving of laser energy; mode control meanscoupled to said position control means for controlling said system tooperate in either said search mode or in one of said first and secondtacking modes; a source of searching signals coupled to said modecontrol means to direct said optical member when said system is in saidsearch mode; receiving means coupled to said optical means and to saidmode control means to control the position of said optical member whensaid system is in said track mode, said receiving means including anarray of infrared energy detectors and scanning means for controllingthe scanning of said detectors with the infrared energy received by saidoptical means so as to respectively provide during operation in saidfirst and second tracking modes a wide field of view or a narrow fieldof view of the target area as a function of the position that the energyis detected relative to the pointing direction of said optical member;means coupled between said receiver means and said mode control meansfor applying switching control signals thereto as a function of thedetection of infrared energy so that said system operates either in saidsearch mode or in one of said first and second track modes; and laserrangefinding means coupled to said optical means for directing laserenergy to said target through said optIcal means and for receiving laserenergy reflected from said target therethrough to provide target rangeinformation.